This invention relates to a heat storage material for storing solar heat, electric power in midnight or the like and a process for producing the same.
When solar heat, electric power in midnight or the like is stored and utilized as a heat source for a heat pump type heater or a hothouse, a substance having a melting point in the temperature range of about 15.degree. to 28.degree. C. is desired as a latent-heat storage material.
It has heretofore been known, for example, disclosed in U.S. Pat. No. 4,189,394, that when a hydrate of calcium chloride (CaCl.sub.2), namely, calcium chloride-hexahydrate (CACl.sub.2.6H.sub.2 O) is used, a heat storage material having a melting point in a relatively low temperature range can be obtained. Since this material has a large amount of latent heat, is incombustible, and causes no environmental pollution, it is excellent as a heat storage material. However, the aforesaid U.S.P. relates to an invention of a nucleating agent, and no description is given therein about a production process. In particular, no description is given therein about a method for adjusting the melting point of a heat storage material so as to be in an arbitrary range of 15.degree. to 28.degree. C.
As a process for producing calcium chloride-hexahydrate, there is known, for example, a process comprising dissolving marble (calcium carbonate; CaCO.sub.3) in hydrochloric acid (HCl) to generate carbon dioxide, evaporating the remaining waste solution, and then taking out the resulting calcium chloridehexahydrate. This process requires the employment of hydrochloric acid, is attended by dangers such as the evolution of carbon dioxide, and is expensive.